Trying to make a python script that runs some bash jobs (for flashing) in separate threads using subprocess.Popen. While running I want to read the stdout of the processes so I can show some progress to the user in a simple curses interface. So each thread runs something like this:
def worker(panel):
panel['status'] = 'STARTING'
panel['process'] = Popen([SCRIPTFILE, panel['ip'], FWFILE, JADFILE, EXEFILE], stdout=PIPE, bufsize=1048576)
panel['status'] = 'RUNNING'
line = " "
while line:
line = panel['process'].stdout.readline()
panel['status'] = line
panel['status'] = 'DONE'
I see in my UI that the status gets stuck on STARTING in this case, but looking at IP traffic it seems that it actually runs but never returns any output. So it seems as Popen actually runs the job but doesn't return. And as soon as the other processes finish it seems it stops hanging and I get all the data at once as it was buffered. I have seen warnings about reading from stdout on a subprocess, but those warnings seem to be related to other scenarios. And I can't really use communicate() instead as it waits for the process to finish. Any idea what could make Popen hang like this?
Tried to make a minimal version showing the problem here (running with python 2.7 on Linux (change find path in script if windows)):
import curses
import time
from subprocess import *
import threading
def check_done(panels):
done = True
for panel in panels:
if panel['status'] != 'DONE':
done = False
break
return done
def flash_worker(panel):
panel['status'] = 'STARTING'
panel['process'] = Popen(["find", "/usr"], stdout=PIPE, bufsize=1048576)
panel['status'] = 'RUNNING'
line = " "
while line:
line = panel['process'].stdout.readline()
panel['status'] = line
panel['status'] = 'DONE'
def ui_worker(panels):
stdscr = curses.initscr()
curses.noecho()
curses.cbreak()
stdscr.keypad(1)
stdscr.scrollok(1)
stdscr.erase()
stdscr.refresh()
while not check_done(panels):
y = 0
stdscr.clear()
stdscr.addstr(y, 0, "IP")
stdscr.addstr(y, 15, "Status")
height, width = stdscr.getmaxyx()
for i in range(0, len(panels)):
y = y + 1
stdscr.addstr(y, 0, "%s" % (panels[i]['ip']))
stdscr.addstr(y, 15, "%s" % (panels[i]['status']))
stdscr.refresh()
time.sleep(0.1)
curses.nocbreak();
stdscr.keypad(0);
curses.echo()
curses.endwin()
def main():
panels = []
for i in range(0,25):
panels.append({ 'ip' : '192.168.0.%d' % (i), 'mac' : '', 'status' : '', 'thread' : None, 'success' : False })
for panel in panels:
panel['thread'] = threading.Thread(name='Panel %s' % (panel['ip']), target = flash_worker, args = (panel,))
panel['thread'].start()
try:
ui_worker(panels)
except KeyboardInterrupt:
print "Caught KeyboardInterrupt, terminating..."
for panel in panels:
panel['thread'].join()
if __name__ == "__main__":
main()
